© ISO 2017 Safety of pressure swing adsorption systems for hydrogen separation and purification Système d’adsorption modulée en pression pour la séparation et la purification de l’hydrogène TECHNICAL[.]
TECHNICAL SPECIFICATION ISO/TS 19883 First edition 2017-03 Safety of pressure swing adsorption systems for hydrogen separation and purification Système d’adsorption modulée en pression pour la séparation et la purification de l’hydrogène Reference number ISO/TS 19883:2017(E) © ISO 2017 ISO/TS 19883:2017(E) COPYRIGHT PROTECTED DOCUMENT © ISO 2017, Published in Switzerland All rights reserved Unless otherwise specified, no part o f this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission Permission can be requested from either ISO at the address below or ISO’s member body in the country o f the requester ISO copyright o ffice Ch de Blandonnet • CP 401 CH-1214 Vernier, Geneva, Switzerland Tel +41 22 749 01 11 Fax +41 22 749 09 47 copyright@iso.org www.iso.org ii © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) Page Contents Foreword iv Scope Normative references Terms and definitions Basic specification Safety requirements of the PSA system 4.1 4.2 4.3 4.4 5.1 Feed stream pressure Working temperature Assembly Material properties 4.4.1 Feed stream pressure 4.4.2 Working temperature General hazards associated with the PSA system 5.1.1 General hazards associated with hydrogen gas 5.1.2 General hazards associated with system leakage 5.1.3 5.2 Hazards related to pressure 5.1.4 Hazards related to ignition o f hydrogen Safety specifications in the field 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6 General hazards Layout considerations Buildings and ventilation Explosion-proof area and explosion-proof grade Electrostatic grounding Flammable and toxic gas detection alarm 5.3 Safety specifications o f equipment and piping 5.3.1 General specification 5.3.2 Safety specifications o f adsorbers 5.3.3 Safety specifications o f the bu ffer tank 5.3.4 Safety specifications o f process control valves 5.3.5 Safety specifications o f piping 5.3.6 Safety considerations for operations and maintenance 10 5.3.7 Safety specifications o f inspection and test 10 5.3.8 Safety specifications o f electrical equipment 11 5.3.9 Safety specifications o f monitoring devices 12 Annex A (informative) Example o f potential locations o f relie f valves 14 Bibliography 15 © ISO 2017 – All rights reserved iii ISO/TS 19883:2017(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work o f preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters o f electrotechnical standardization The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part In particular the different approval criteria needed for the di fferent types o f ISO documents should be noted This document was dra fted in accordance with the editorial rules of the ISO/IEC Directives, Part (see www.iso org/directives) Attention is drawn to the possibility that some o f the elements o f this document may be the subject o f patent rights ISO shall not be held responsible for identi fying any or all such patent rights Details o f any patent rights identified during the development o f the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso org/patents) Any trade name used in this document is in formation given for the convenience o f users and does not constitute an endorsement For an explanation on the meaning o f ISO specific terms and expressions related to formity assessment, as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html This document was prepared by Technical Committee ISO/TC 197, Hydrogen technologies iv © ISO 2017 – All rights reserved TECHNICAL SPECIFICATION ISO/TS 19883:2017(E) Safety of pressure swing adsorption systems for hydrogen separation and purification Scope This document identifies sa fety measures and applicable design features that are used in the design, commissioning, and operation o f pressure swing adsorption systems for hydrogen separation and purification It applies to hydrogen pressure swing adsorption systems that process all kinds o f impure hydrogen streams as feed, including both stationary and skid-mounted pressure swing adsorption systems for hydrogen separation and purification in commercial or industrial use This document also applies to small-scale PSA hydrogen system installed within containers, where allowed by local regulations The scope of this document includes the equipment depicted within the dashed lines in Figure Figure — Example o f typical equipment in PSA system for hydrogen separation and purification Normative re ferences The following documents are re ferred to in the text in such a way that some or all o f their content constitutes requirements o f this document For dated re ferences, only the edition cited applies For undated re ferences, the latest edition o f the re ferenced document (including any amendments) applies ISO 4126-1, Safety devices for protection against excessive pressure — Part 1: Safety valves ISO 11114-1, Gas cylinders — Compatibility of cylinder and valve materials with gas contents — Part 1: Metallic materials ISO 11114-2, Gas cylinders — Compatibility of cylinder and valve materials with gas contents — Part 2: Non-metallic materials ISO 11114-4, Transportable gas cylinders - Compatibility o f cylinder and valve materials with gas contents — Part 4: Test methods for selecting metallic materials resistant to hydrogen embrittlement IEC 60079-0, Explosive atmospheres — Part 0: Equipment — General requirements IEC 60079-10-1, Explosive atmospheres — Part 10-1: Classification of areas — Explosive gas atmospheres IEC 60079-14, Explosive atmospheres — Part 14: Electrical installations design, selection and erection IEC 60204-1, Safety of machinery — Electrical equipment of machines — Part 1: General requirements © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) IEC 60529, Degrees of protection provided by enclosures (IP Code) IEC 60364-4, Low-voltage electrical installations — Part 4: Protection for safety NFPA 56, Standard for Fire and Explosion Prevention during Cleaning and Purging of Flammable Gas Piping Systems Terms and definitions For the purposes o f this document, the following terms and definitions apply ISO and IEC maintain terminological databases for use in standardization at the following addresses: — IEC Electropedia: available at http://www.electropedia org/ — ISO Online browsing platform: available at http://www.iso org/obp 3.1 pressure swing adsorption method PSA method gas separation method that takes advantage of the selective adsorption of a solid adsorbent (3.5) for di fferent gases and the ability o f solid adsorbents to adsorb more impurities at high pressure and to reject impurities at low pressure Note to entry: PSA, as practiced commercially, is a batch process utilizing multiple adsorbent-loaded vessels for the continuous purification o f a gas stream 3.2 vacuum pressure swing adsorption system for hydrogen separation and purification that relies on desorption at sub-atmospheric pressure (achieved with vacuum pumps) to improve the per formance o f the system 3.3 pressure swing adsorption system for hydrogen separation and purification hydrogen generation system that separates and purifies hydrogen from an impure hydrogen stream through the pressure swing adsorption process 3.4 adsorber vessel in which the adsorbent (3.5 ) used for hydrogen separation and purification is contained, which can be vertical vessels 3.5 adsorbent solid materials used to adsorb gas impurities from the impure hydrogen streams, thereby realizing the separation o f the hydrogen from the other gases 3.6 process control valves operational devices that can open or close to regulate flow in response to a signal from the system (3.7) control 3.7 control system system that per forms operations such as opening and closing process control troubleshooting, product quality control, or optimization o f process parameters valves (3.6), system © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 3.8 tail gas gas remaining a fter the impure hydrogen mixture is purified through the PSA system Note to entry: Other names for tail gas are desorbed gas, purge gas, or o ff gas 3.9 stationary PSA system for hydrogen separation and purification PSA system in which all equipment and piping are permanently mounted to the equipment foundation(s) and piping support structure 3.10 skid-mounted PSA system for hydrogen separation and purification PSA system in which some or all o f the equipment and piping are a ffixed to one or more skids, or moveable bases 3.11 fire separation distance distance between the PSA system and nearby buildings (3.15 ) that is required in order to prevent fire rom spreading from a PSA system to nearby buildings f 3.12 buffer tank vessel that receives the desorbed gas from the adsorbers (3.4) (PSA system) or from the vacuum pumps (3.13 ) (VSA system) and minimizes the composition and pressure variation of the desorbed gas Note to entry: A bu ffer tank may also be re ferred to as a surge drum 3.13 vacuum pump device used for evacuating the adsorbers (3.4) during the desorption stage, allowing the adsorbents (3.5) to be desorbed and regenerated at sub-atmospheric pressure to improve per formance o f a PSA system 3.14 container enclosed construction or bracing structure fabricated to avoid the e ffects o f specific environmental and climatic conditions, or protect personnel and livestock from accidental contact with the dangerous components o f a small hydrogen PSA system 3.15 building structure that has a roof and walls, with the similar function as a container (3.14) for a hydrogen PSA system or the components o f a hydrogen PSA system 3.16 hydrogen embrittlement degradation o f metal material properties due to the presence o f a hydrogen environment Basic specification 4.1 Feed stream pressure PSA systems for hydrogen generation and purification typically have feed gas pressures ranging from 0,3 MPa to 6,0 MPa The operating pressure cycles from full feed gas pressure during adsorption to near atmospheric pressure (0,03 MPa) or vacuum (−0,09 MPa) during desorption © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 4.2 Working temperature The normal working temperature is between °C and 40 °C for a PSA system for hydrogen separation and purification 4.3 Assembly A PSA system for hydrogen separation and purification can be stationary or skid-mounted based on the end use o f the hydrogen product and on the hydrogen throughput Small PSA systems may be installed within containers, i f allowed by local regulations 4.4 Material properties 4.4.1 Feed stream pressure Metallic and non-metallic materials used in the construction of internal or external parts of a PSA thermal conditions, both test conditions and operating conditions, for the design lifetime of the equipment The compatibility o f materials shall be evaluated to comply with ISO 11114-1, ISO 11114-2, ISO/TR 15916 or local regulations system for hydrogen separation and purification should be suitable for all physical, chemical, and 4.4.2 Working temperature When ferrous metal is used in a PSA system, adequate consideration and analysis shall be taken according to ISO/TR 15916, ISO 11114-4 or the local regulations For the non-metal materials contacting with hydrogen, the hydrogen permeability shall be considered Safety requirements of the PSA system 5.1 5.1.1 General hazards associated with the PSA system General hazards associated with hydrogen gas Hydrogen is colourless, odourless, and highly flammable; it burns with a nearly invisible flame in daylight It can form an explosive mixture with air, and its lower and upper explosive limits in air are % and 75 % (percent by volume) at atmospheric temperature and pressure Hydrogen in air will displace oxygen and may result in asphyxia i f the partial pressure o f oxygen in air reduces due to high hydrogen concentration 5.1.2 General hazards associated with system leakage Due to its low molecular weight and small size, hydrogen leaks easily from flanges and other sealing sur faces (e.g vent valves) Hydrogen is highly buoyant due to its low specific gravity, and it can form large areas o f flammable or explosive gas Because hydrogen is colourless, the extent o f a flammable area is not readily identifiable 5.1.3 Hazards related to pressure Normal pressure swings during the PSA process will cause alternating stress on the adsorbers, process control valves, and piping, which could lead to cracks in the vessels or piping or to another failure mode The failure o f hydrogen PSA equipment or piping can result in the rapid release o f energy due to the high pressure o f the equipment The resulting shock wave may damage surrounding equipment © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 5.1.4 Hazards related to ignition of hydrogen Ignition o f hydrogen due to a leak to atmosphere from a hydrogen PSA system will cause energy/heat release or explosion As heat is released through combustion o f hydrogen, the gas within the PSA system will expand due to the increase in external temperature, and the material properties o f the PSA system may degrade The combination o f increasing temperature and pressure and degradation o f the material properties could cause piping or vessel failure 5.2 Safety specifications in the field 5.2.1 General hazards Feed gases o f the PSA systems for hydrogen separation and purification include syn-gas generated from natural gas, ammonia cracking gas, coal gas, coke oven gas, ammonia tail-gas, methanol o ff-gas, refinery o ff-gas, etc., and the hydrogen content may be more than 25 % The oxygen content in the feed stream shall be restricted to ensure combustible gases, such as hydrogen, are away from their flammable limit PSA hydrogen systems shall be sited according to the requirements o f the applicable national sa fety standards and the construction and materials requirements shall be based on the partial pressure of hydrogen PSA designs shall account for all circumstances that are anticipated during the li fe o f their operation The PSA control system should be designed to move the PSA to a sa fe state on detection o f a failure via the PSA control system A fire protection system shall be considered for a hydrogen PSA system Possible fire protection measures include a means to shut down the PSA quickly (either automatic or manual), a sprinkler system, a deluge system, or a dry-chemical extinguishing system Small fires may be extinguished by dry-chemical extinguishers, carbon-dioxide extinguishers, nitrogen, or steam Water may be used to cool equipment adjacent to a hydrogen fire 5.2.2 Layout considerations The layout o f equipment and buildings associated with a PSA system for hydrogen separation and purification shall form to local requirements for fire separation distance When a valve skid is designed such that the piping and valves are arranged in multiple levels that cover a large horizontal area, platforms constructed o f steel grating should be used to prevent a confined space where hydrogen could build a flammable atmosphere A PSA hydrogen system installed within a container shall be designed and constructed to avoid any reasonably foreseeable risk o f fire or explosion posed by the system itsel f, or by the feed gas, product gas, or tail gas The containers shall have the strength, stability, durability, resistance to corrosion, and other physical properties to support and protect all PSA hydrogen system components and piping Containers should also meet the requirements o f storage, transport, installation, and final location conditions in accordance with ISO 16110-1 or other applicable national or local regulations Containers intended for indoor use shall be designed and tested to meet a minimum degree of protection o f IP 20 as per IEC 60529 The PSA hydrogen system used in outdoor locations shall be designed and tested to meet a minimum degree of protection of IP 44 as per IEC 60529 5.2.3 5.2.3.1 Buildings and ventilation General Small PSA systems for hydrogen separation and purification may be enclosed within a building Other equipment associated with hydrogen PSA systems may be enclosed within one or more standalone buildings Examples include valve skids, vacuum pump for desorbed gas, control systems, and analyzers © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 5.2.3.2 Buildings Buildings shall be designed to the appropriate hazardous area designation based on the potential for hydrogen to be present due to leaks or other breakdown (e.g Zone per IEC 60079-10-1) The distances between buildings, structures and equipment shall comply with local requirements for fireproo f distance Enclosed buildings, i f utilized, shall be designed as explosion-proo f type Alternately, for non-explosion proo f buildings, the ratio between the pressure relie f area and the building volume shall comply with local regulations The area used for pressure relief could be a light roof, a wall, a door, or a window 5.2.3.3 Ventilation of buildings Buildings shall be designed with ventilation equipment that is interlocked with flammable or toxic gas detectors When the provided ventilation influences the type o f area classification, that area should be purged with a minimum o f five air changes prior to energizing the devices Alternatively, the system may be provided with composition measurement capabilities that control the amount of purging required to achieve levels below 25 % of the LEL Purging need not be performed if the atmosphere within the compartment and associated ducts can be demonstrated by design to be non-hazardous Appropriate methods shall be adopted to prevent non-essential staff from entering buildings and approaching equipment The main entrance shall be constructed according to applicable specifications and regulations Fire-fighting equipment shall be readily accessible Any building that sta ff can enter shall be equipped with an emergency exit opening outwards Any door with a latch should be equipped with a rapid unlocking mechanism such that the door can be opened without delay 5.2.3.4 PSA hydrogen systems installed within containers Containers housing PSA hydrogen systems shall be mechanically ventilated Failure o f ventilation, confirmed by measurement o f flow, pressure, or the current o f the ventilating device, shall trigger an audible or visible alarm and may trigger a PSA hydrogen system shutdown In systems intended for outdoor use, containers may be positive pressure ventilated as per IEC 60079-2 or other applicable code or regulation The maximum concentration o f any flammable gas in the system ventilation exhaust should be below 25 % of the LFL during all operation conditions 5.2.4 Explosion-proof area and explosion-proof grade Classification o f all areas associated with the hydrogen PSA system that have an explosion hazard shall comply with IEC 60079-10-1 or other applicable local regulations Outdoor areas near PSA equipment and well-ventilated areas inside buildings shall be classified based on the potential for hydrogen to be present due to leaks or other breakdown (e.g Zone per IEC 60079-10-1) The explosion-proof grade of electrical equipment should not be lower than the grade and group of explosive hydrogen mixture: IIC T1 Electrical equipment and wiring in areas with explosion hazard shall be selected and configured in accordance with IEC 60079-0 and IEC 60079-14 or other applicable local code or regulations © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 5.2.5 5.2.5.1 Electrostatic grounding General Electrostatic grounding shall be carried out for the objects that can result in electrostatic hazard because the PSA system for hydrogen separation and purification may generate and accumulate static electricity Dedicated electrostatic grounding connectors shall have a resistance to ground according to the requirements of IEC 60204-1, IEC 60364-4 or applicable local code or regulations When other grounding devices are used for electrostatic grounding, their grounding resistances shall be selected based on applicable local code or regulations covering such grounding devices 5.2.5.2 Adsorber and buffer tank Enclosures o f adsorber, bu ffer tank and other stationary pressure vessels shall be subject to electrostatic grounding Equipment with diameter of not less than 2,5 m and volume of not less than 50 m3 should have at least two grounding points and the grounding points should be evenly distributed along the periphery o f the equipment with an interval o f not more than 30 m 5.2.5.3 Piping system Electrostatic grounding should be provided at the inlet and outlet o f the unit, at the boundary o f areas with di fferent explosion hazards, at pipe branches, and every 80 m to 100 m along straight pipes When the net distance between parallel pipes is less than 100 mm, jumpers should be provided every 20 m to prevent a spark jumping from one pipe to another When the distance between two pipes that cross each other is less than 100 mm, a jumper should be provided where the pipes cross Metal flanges fastened with metal bolts or clamps are usually not provided with additional electrostatic wire, but it is required to ensure good conductive contact between four bolts or clamps at a minimum 5.2.6 Flammable and toxic gas detection alarm Combustible gas detectors shall be installed in unit areas When toxic gas exists and may result in injuries to personnel i f leaks form, toxic gas detector(s) shall be installed The monitoring points should be located at such places where gas tends to accumulate and sampling and detection can be carried out easily in accordance with physical and chemical properties o f gases, features o f release source, layout o f production area, geographical conditions, environment and climate, operation and inspection routes, etc Some o f the places where combustible or toxic gas leakage or accumulation may occur: — seals o f vacuum pumps or compressors; — gas sampling ports and associated analysers; — drains and vents; — equipment or piping flanges; — valve packing; — buildings or containers associated with the PSA system When combustible gas in the air is 25 % of its lower explosive limit, or when the toxic gas concentration reaches 25 % of the permissible exposure limit, audible and visual detection alarm shall be activated at site In addition, the alarm signal shall be sent to the control room or operation room The number o f flammable and toxic gas monitoring points should depend on the location o f possible release sources and the ventilation conditions © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) 5.3 Safety specifications o f equipment and piping 5.3.1 General specification Adsorbers are the primary components o f the PSA system for hydrogen separation and purification, and their per formance determines the per formance o f the PSA system The vessel dimensions, internal component design, and adsorbent selection and amount are chosen to optimize hydrogen recovery rate and manu facturing cost, to prevent adsorbent leakage and particle fluidization, and to ensure mechanical strength within the design li fe cycle 5.3.2 5.3.2.1 Safety specifications o f adsorbers General Individual adsorbers o f hydrogen PSA systems are in cyclic service and will typically withstand about million cycles a fter 10 to 20 years o f operation So fatigue is an important mode o f failure to be considered, aggravated by the presence o f hydrogen An adsorber is designed for a given pressure and number o f cycles, and especially all assemblies are designed according the corresponding S-N curve, as weld joints are primarily areas o f crack initiation due to fatigue The main parameters that affect fatigue resistance of adsorbers, except intrinsic stress variation for PSA process, are the e ffect o f exposure to hydrogen (called hydrogen embrittlement), weld quality, and abrication quality (e.g peaking, misalignment, and corrosion fatigue) f 5.3.2.2 Hydrogen embrittlement The susceptibility to hydrogen embrittlement is strongly dependent on the materials’ strength properties and hydrogen environment Gaseous hydrogen embrittlement generally occurs at close to ambient temperatures for carbon steel In combination with the cyclic fatigue mechanism through fluctuating bending stresses (i.e pressures) in the PSA system with the presence o f atomic hydrogen in dislocations causes accelerated crack growth The greater the hydrogen purity, the more pronounced the embrittling e ffect since the impurities most requently encountered in hydrogen (i.e traces o f oxygen and water vapour) have an inhibiting e ffect on f embrittlement Sulfur dioxide and carbon monoxide also have an inhibiting effect Other impurities (e.g methane, nitrogen) not seem to have any appreciable e ffect Some impurities (e.g carbon dioxide and especially hydrogen sulfide) have an accelerating e ffect on hydrogen embrittlement The parameters that should be considered related to hydrogen embrittlement are the environment (i.e operating conditions), the design, and sur face condition and the materials As hydrogen embrittlement is similar to a stress corrosion phenomenon, the stress level is of paramount importance All forms of stresses (e.g thermal, pressure, mechanical, etc.) should be considered in a hydrogen PSA system 5.3.2.3 Geometric discontinuities (peaking) Geometric discontinuities are also important as they can create high local stress that will reduce significantly the fatigue li fetime o f the vessel Geometric discontinuities include those created by manufacturing tolerances (e.g misalignment, peaking, out of roundness) which are here much more critical than for a static vessel Peaking is a deviation from a true circular shape located along a longitudinal weld of a shell Taking peaking into account requires measuring the distance “delta” to theoretical circle (outside = “roof” shape or inside = “heart” shape) © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) For defining the maximum acceptable peaking size, pressure vessel codes, such as ISO 16528-1 or local applicable code or regulations, should be consulted 5.3.2.4 Corrosion Under some conditions in a hydrogen PSA system, adsorbers could be a ffected by internal corrosion in case o f the presence o f condensate in the bottom head, even in the presence o f hydrogen In the presence o f corrosion and pressure cycling conditions, a crack could be initiated at corrosion pit and could be propagated by fatigue 5.3.2.5 Design and manufacture The design and manu facture o f the adsorber should comply with the appropriate local and national pressure vessel regulations, and consideration shall be given to the impact of alternating stress If not, there is chance of failure or damage in the vessels because of accumulation of plastic strain The welding o f any plate on the adsorbers should be minimized, and when per formed, the e ffect on the alternating stress should be evaluated Gaskets should be selected to prevent leakage from the adsorber vessels during normal operation and to withstand the change in conditions during startup and shutdown 5.3.3 Safety specifications o f the buffer tank The manufacture of the buffer tank should conform to the requirements of ISO 16528-1 or to local regulations In cases where buffer tanks with different operating pressures are connected, the buffer tank with the lowest operating pressure shall not be operated at overpressure under any condition Bu ffer tanks should be located such that there is no direct impact on adjacent tanks in the event o f leakage from the buffer tank(s) A separate sa fety system should be installed for each bu ffer tank i f it is possible to isolate them or i f their design pressures differ If there is no potential for the buffer tanks to be isolated from each other, a single sa fety system may be used i f the design pressure o f the vessels is identical or i f the sa fety system is designed to maintain the pressure below the lowest bu ffer tank design pressure 5.3.4 Safety specifications o f process control valves Process control valves act frequently The failure o f process control valves may result in whole system mal function, adsorbents damage, or equipment overpressure During the PSA design phase, consideration should be given to selecting control valves that will have minimal leakage over the life of the valve 5.3.5 5.3.5.1 Safety specifications o f piping General specification Materials for pipe and pipe fittings o f the PSA system for hydrogen separation and purification should be selected in accordance with the requirements set forth in the appropriate local and national pressure piping specifications 5.3.5.2 Piping design In the design o f piping directly connected to the adsorbers, for example, the piping between adsorbers and process control valves, consideration should be given to the impact o f alternating stress (caused by the frequent pressure change) on the pipe strength © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) Pipe sections under thermal expansion and contraction should be designed and laid out based on flexibility calculations and thermal compensation requirements The piping system should be equipped with nitrogen purging facilities Pipe supports should be designed and located in accordance with the requirements set forth in the appropriate local and national pressure piping regulations 5.3.5.3 Safety relie f devices I f the design pressure o f the PSA system piping or vessels is less than the upstream or downstream design pressure or i f the PSA system is subject to a fire or other thermal relie f case, relie f valves may be required to protect the PSA system equipment Common locations for relie f valves are downstream of the feed stream inlet shut-off valves and on the buffer tank(s) (see Figure A.1) Any relief valves shall comply with ISO 4126-1 or other applicable local code or regulations 5.3.6 Safety considerations for operations and maintenance Because hydrogen PSA systems contain flammable and/or toxic gas during normal operation, thorough purging o f the PSA system prior to maintenance and be fore returning the system to service is essential For this reason, hydrogen PSA systems shall be designed with su fficient vents to enable purging o f the PSA system Dead legs should be minimized since pockets o f trapped gas can be di fficult to remove Consideration should be given on the direction in which gas will flow Purging is typically conducted in a top-down direction to avoid migration o f water from the lower layer(s) o f adsorbent onto the upper layer(s) Hydrogen PSA systems are typically purged with nitrogen The PSA system design should include connections to enable flow o f nitrogen into the piping and vessels PSA system designs should include connections at the appropriate locations to facilitate nitrogen purging during adsorbent removal I f any portion o f the PSA system being purged is located indoors, precautions shall be taken during purging and when checking oxygen or flammable gas levels to prevent flammable gas build up or oxygen deficient condition within the building or enclosure Prior to maintenance, purging shall reduce the flammable gas concentration to less than 25 % o f the LEL according to NFPA 56 or to the level prescribed by local code or regulations Be fore placing the PSA system in operation, the oxygen level shall be reduced to 60 % o f the minimum oxygen (limiting oxidant) concentration required to support combustion There is a particular risk o f air ingress into the feed stream when operating the PSA system at sub- atmospheric pressures 5.3.7 5.3.7.1 Safety specifications o f inspection and test Non-destructive testing 100 % non-destructive testing should be applied to welds of the piping where connected to adsorber vessels because those welds are subjected to cyclic stress The testing method should accord with ISO 17636-1 or local requirements The grade of welding should be in accordance with ISO 5817, ISO 3834-1, ISO 3834-2 or related local regulations 5.3.7.2 Principle o f pressure testing Hydraulic testing is pre ferred for piping pressure tests When pneumatic pressure testing is used on piping, test procedure and appropriate sa fety measures should be taken as required by ISO 15649 or local requirements 10 © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) When pressure testing a section of piping that contains instrumentation, the test pressure shall not exceed the maximum allowable test pressure of the instruments unless the instruments are removed When the design temperature of the piping surpasses the test temperature, the test pressure should be calculated based on applicable local or national regulations 5.3.7.3 Pressure test 5.3.7.3.1 Preparations before test Various certificates o f formity and technical documents, including all test records and certificates, drawings, inspection certificates for the adsorber vessels and bu ffer tanks, should be checked for completeness prior to the pressure test, and the test should be carried out only a fter the a foresaid certificates and documents are verified to be correct Visual inspection should be conducted a fter assembly o f the PSA system is completed to check the relevant dimensions o f the system, to veri fy the correct connections o f the various piping and electrical circuits and to evaluate the general appearance o f the system 5.3.7.3.2 Strength test The PSA system for hydrogen separation and purification should be tested according to the local and national vessel and piping codes Testing of individual components shall be acceptable, with connection joints being subject to ISO 5817 or the appropriate pressure vessel code requirements 5.3.7.3.3 Vacuum test A fter the strength test, vacuum systems should be subject to vacuum for 24 h The air tightness and degree of vacuum should be in accordance with local code or regulations 5.3.7.3.4 Container ventilation testing Ventilation systems o f containers or buildings that house hydrogen PSA systems shall be tested to veri fy that they form to local code or regulations The hourly air exchange rate with the exhaust fan in operation should be verified To veri fy the e ffectiveness o f the ventilation, the flammable or toxic gas sensor should be located based on where the gas will accumulate If the electric equipment and wires of the electrical container are not explosion proof, the electrical container should undergo a pressure test at 1,0 kPa and should be considered qualified i f there is no leakage 5.3.8 Safety specifications o f electrical equipment Electrical facilities in hydrogen generation areas should be protected in accordance with IEC 60079-10- or other applicable local or national electrical code Outdoor areas and areas within well-ventilated buildings should be classified based on the potential for hydrogen to be present due to leaks or other breakdown (e.g Zone per IEC 60079-10-1) Electrical equipment and associated wiring in areas with explosion hazards should be selected and configured in accordance with IEC 60079-0 and IEC 60079-14 or other applicable local or national electrical code All metal enclosures, piping, bases, or frames should be grounded and comply with IEC 60204-1 and IEC 60364-4 or other applicable local or national electrical code © ISO 2017 – All rights reserved 11 ISO/TS 19883:2017(E) 5.3.9 Safety specifications o f monitoring devices 5.3.9.1 General specification Key parameters during operation should be continuously monitored In case o f a failure, the monitoring system should initiate alarms and/or shutdown interlocks Instrumentation design and specifications should comply with the requirements o f IEC 61508 or other applicable local regulations or code 5.3.9.2 5.3.9.2.1 Monitoring devices Pressure measuring instruments Pressure monitoring data provide the main basis for the control system to determine the operational status o f the PSA system These instruments monitor the pressure during adsorption and desorption to ensure proper operation and to identi fy equipment failure Pressure o f the following items may be monitored: feed gas, adsorbers, hydrogen product, bu ffer tank(s), instrument air, etc Overpressure may appear in a PSA hydrogen system under the following conditions: — open-close valves between vessels at di fferent operational pressure level fail to close; — modulating control valve fails to open or close or moves to an incorrect position; — PSA system outlet block valves are closed, and the feed to the PSA is supplied by a compressor 5.3.9.2.2 Temperature measuring instruments Temperature measurements are used to correct the computation o f feed gas and product hydrogen flow rate and may be used to monitor or control the adsorption process during operation 5.3.9.2.3 Gas composition analysis instruments To ensure that the oxygen level does not result in a flammable or explosive mixture, online oxygen analysis should be provided on the feed gas and desorbed gas piping o f hydrogen PSA systems i f the feed can contain enough oxygen to result in a hazardous mixture in either the feed or desorbed gas stream 5.3.9.2.4 Valve position sensor Process control valves may be provided with a valve position sensor that sends the valve position to the control system to prevent a high-pressure stream from leaking into a low-pressure stream For open/close valves, the position sensor is a switch that indicates if the valve is in a given position (open or closed) 5.3.9.3 Automatic interlock shutdown control system I f one o f the monitoring devices o f a PSA system for hydrogen separation and purification sends out an alarm signal, an investigation should be carried out The cause o f the alarm should be identified and the issue resolved such that normal operation is resumed In order to maintain sa fe operation o f the PSA system, it may be shut down for inspection i f one o f the following conditions occurs — pressure, temperature, compositions or flow rate o f feed gas exceeds the alarm set point; — a process control valve fails during operation or internal valve leakage occurs and cannot be isolated; — the hydrogen concentration in the air exceeds %; — power supply o f the PSA system fails; 12 © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) — the pressure o f the instrument air reaches its interlock value; — oxygen content in a feed stream or in piping with the vacuum desorption process exceeds the permissible limit; — pressure o f bu ffer tank exceeds the maximum allowable set point; — vessel or piping leaks to the atmosphere; — toxic gas concentration in the air exceeds the allowable value A hazard review should be conducted to identi fy the alarms and interlocks that are required to provide sa fe operation o f the PSA system Other failures in the PSA system or in upstream or downstream operating units may also necessitate the shutdown o f the PSA system © ISO 2017 – All rights reserved 13 ISO/TS 19883:2017(E) Annex A (informative) Example o f potential locations o f relie f valves Key inlet shut-off valve relief valve feed gas outlet shut-off valve of gas-liquid separator feed gas buffer adsorbers 10 11 vacuum pump buffer tank surge drums product tail gas Figure A.1 — Potential locations o f relief valves 14 © ISO 2017 – All rights reserved ISO/TS 19883:2017(E) Bibliography [1] ISO 3834-1, Quality requirements for fusion welding o f metallic materials — Part 1: Criteria for the selection o f the appropriate level o f quality requirements [2] ISO 3834-2, Quality requirements for fusion welding of metallic materials — Part 2: Comprehensive [3] ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding [4] [5] [6] [7] [8] ISO 15649, Petroleum and natural gas industries — Piping ISO/TR 15916, Basic considerations for the safety of hydrogen systems ISO 16110-1, Hydrogen generators using fuel processing technologies — Part 1: Safety ISO 16528-1, Boilers and pressure vessels — Part 1: Performance requirements ISO 17636-1, Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray quality requirements excluded) — Quality levels for imperfections techniques with film [9] IEC 60079-2, Explosive atmospheres — Part 2: Equipment protection by pressurized enclosure “p” [10] IEC 61508, Functional safety ofelectrical/electronic/programmable electronic safety-related systems © ISO 2017 – All rights reserved 15 ISO/TS 19883:2017(E) ICS 71.100.20 Price based on 15 pages © ISO 2017 – All rights reserved